one way is with a lathe and metal spinning equipment, metal spinning is an interesting process, you can watch videos of it on youtube
another way, although possibly crude, is to use one of those small SS garden globe ornament balls, the inside sphere is of much smaller diameter
from the picture of stans spherical cell i might guess it was 3" in diameter
i don't think these cells would be worth anything more than as a demo cell and as a learning experience, tube cells are much more practical for an actual application, as evidenced by Stans progress, his finial developments were for modular stackable self contained resonant cavity units, and then water fuel injectors, these two systems are the final business systems
that being said, the learning potential should not be overlooked from studying and experimenting with this design configuration
